Spark ignition systems



Nov. 12, 1968 l B. GILBERT 3,410,257

SPARK IGNITION SYSTEMS Filed March 9, 1966 2 Sheets-Sheet 1 B WDISTRIBUTOR -{PLUGS '6 J 2s .4 l .5

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Nov. 12, 1968 Filed March 9, 1966 B. GILBERT SPARK IGNITION SYSTEMS 2Sheets-Sheet; 2'

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United States Patent 3,410,257 SPARK IGNITION SYSTEMS Brian Gilbert,Sutton Coldfield, England, assignor to Joseph Lucas (Industries)Limited, Birmingham, England Filed Mar, 9, 1966, Ser. No. 533,000 Claimspriority, application Great Britain, Mar. 11, 1965, 10,330/ 65 12Claims. (Cl. 123148) ABSTRACT OF THE DISCLOSURE In spark ignitionapparatus of the capacitor discharge type switch means is driven by theengine between open and closed conditions. When the switch means isclosed, energy is stored in a storage inductor and in a controlinductor, which can be constituted by the storage inductor or a separateinductor. When the switch means opens, the storage inductor transfersits energy to a storage capacitor, and the control inductor transfersits energy to a control capacitor, which where the storage inductorconstitutes the control inductor will be constituted by the storagecapacitor. Once the control capacitor has charged, it starts todischarge, and means is provided operable by this discharge for turningon a switch to permit the storage capacitor to discharge through theswitch to produce the required spark.

This invention relates to spark ignition systems.

A spark ignition system according to the invention comprises incombination first and second terminals which in use are connected to aDC. source, a storage inductor connected across said terminals in aseries circuit including switch means which is turned on and off intimed relationship with the engine, so that when the switch means isclosed energy is stored in the inductor, a storage capacitor to whichthe energy stored in the inductor is transferred when the switch meansopens, and means operable while the switch means is still open forturning on a switch providing a discharge path for the capacitor,discharge of the capacitor through the switch producing a spark.

In the accompanying drawings, FIGURES 1 to 4 are circuit diagramsillustrating four examples of the invention.

Referring to FIGURE 1, there are provided terminals 11, 12 which in useare connected to a DC. source so as to be negative and positive inpolarity respectively. The terminals are interconnected through a seriescircuit including resistors 13, 14 and an interruptor .15 which isdriven by the engine. A point intermediate the resistors 13, 14 isconnected to the base of a transistor 16, the emitter of which isconnected to the terminal 11, and the collector of which is connected tothe terminal 12 through an inductor 17 in series with a resistor 18. Thecollector and emitter of the transistor are bridged by a capacitor 19.

The collector of the transistor 16 is connected to the terminal 12through a capacitor 21 in series with a diode 22, and is also connectedto the anode of a controlled rectifier 23 through the primary winding 24of an ignition transformer 25 the secondary winding 26 of which isconnected through a distributor 27 to the spark plugs 28 of the enginein turn. The cathode of the rectifier 23 is connected to the terminal 12through the diode 22 and a resistor 29 in parallel and the gate of therectifier 23 is connected to the terminal 12 through a resistor 31.

In use, when the interruptor 15 closes the transistor 16 can conduct,and the rectifier 23 is reverse biased so that it cannot conduct.Current flows through the transistor 16 to the inductor 17, so thatenergy is stored in the inductor. When the interruptor 15 opens, thetransistor 16 ceases to conduct, and current flows from the inductor 17through the capacitor 21 and diode 22 so that the capacitor 21 ischarged. While the capacitor 21 is being charged, the voltage dropacross the diode 22 maintains the gate of the rectifier 23 negative withrespect to its cathode, so that the rectifier 23 cannot conduct.However, when the capacitor 21 is charged to its peak voltage, currentbegins to flow from the capacitor 21 back into the inductor 17, and sothe diode 22 becomes reverse biased, at which point current is divertedthrough the resistor 31 and the gate and cathode of the rectifier 23, sothat the rectifier 23 is caused to conduct. The capacitor 21 nowdischarges through the winding 24 and the anode and cathode of therectifier 23, and the high voltage induced in the winding 26 producesthe required spar-k. For many practical purposes, the spark can beconsidered to be produced instantaneously when the interruptor 15 opensif it occurs not later than microseconds after the interruptor opens.

The capacitor 19 has a capacitance which is small compared with that ofcapacitor 21 and is included to allow for energy stored in any strayinductance in the circuit, and to absorb any transients when the sparkis produced. The resistor 18 can in some circuits be constituted by theresistance of the inductor 17 itself, and the resistor 29 is preferablyincluded to ensure that the capacitor 21 is completely discharged at theend of each cycle.

Although in FIGURE 1 the transistor 16 is controlled by an interruptor15, it will be appreciated that it can be controlled by an deviceoperated by the engine. For example, the interrupt 15 could be asemi-conductor switch controlled by pulses from a magnetic generatoroperated by the engine.

It will be appreciated that at the end of a cycle when the interruptor15 closes again, conduction of the transistor 1'6 reverse biases therectifier 23, so that there is no danger of the rectifier 23 continuingto conduct.

The core of the inductor 17 may be designed to a saturate or start tosaturate when the current exceeds a predetermined value to preventgeneration of excessive voltages. Alternatively, or in addition, aresistor with a largepositive temperature co-efficient can be connectedin series with the inductor 17.

FIGURE 2 shows the separate modifications of the example shown inFIGURE 1. Firstly, the diode 22 is re-positioned in the series circuitincluding the inductor 17 and resistor 18, and secondly the winding 24and capacitor 21 are connected to the collector of the transistor 16through a diode 32 and resistor 33 in parallel.

Ignoring for the moment the diode 32 and resistor 33, the circuitoperates in much the same way as FIGURE 1. However, in FIGURE 1, whenthe transistor 16 is switched off, there is a slight delay before theinductor 17 discharges its energy into the capacitor 21, because thediode 22 is not conducting when the transistor 16 is switched off. InFIGURE 1, this delay is allowed for by the capacitor 19. In FIGURE 2,however, the diode 22 is conducting when the transistor 16 is switchedoff, so there is no delay in transferring the energy from the inductor17 t0 the capacitor 21. Moreover, in FIGURE 2, in the event of anaccidental reclosure or breakdown on the interruptor 15 before thecapacitor 21 is fully charged, the controlled rectifier 23 will not betriggered because the diode 22 will continue to conduct, somaintainingthe negative bias on the gate of the rectifier 23. In FIG- URE 1,accidental reclosure may reverse bias the diode 22 and cause therectifier 23 to conduct before there is sufiicient charge on thecapacitor 21 to produce the spark, and the rectifier 23 may still beconducting when the contacts finally separate so that there can be nofurther build up of voltage on the capacitor 21. In FIGURE 2, (stillignoring the diode 32 and resistor 33) the energy stored in thecapacitor 21 is lost by discharge through the transistor 16 in the eventof accidental reclosure, but the residual energy stored in the inductor17 is still available to produce the spark when the interrupter opensproperly.

In order to prevent the capacitor 21 from discharging through thetransistor 16 in the event of accidental reclosure, the diode 32 can beincluded, and in this case the connection from the gate of the rectifier23 is preferably made to a point intermediate the resistor 18 andinductor 17. The rectifier 23 is now switched on when the capacitor 19reaches its peak voltage and commences to discharge back into theinductor 17. However, since the capacitors 19, 21 reach their peakvoltage at substantially the same time, the timing of the circuit is noimpaired. It will be appreciated that accidental reclosure now resultsonly in the loss of energy from the capacitor 19, which is relativelyunimportant.

The diode 32 has the additional advantage that it prevents damage to thetransistor 16 which might result from the discharge of the capacitor 21through the transistor 16.

In some cases the rectifier 23 may be sufiiciently sensitive forswitching on to occur without the assistance of the capacitor 19, as aresult of the self-capacitance of the diode 32.

The resistor 33 in FIGURE 2 takes the place of the resistor 29 in FIGURE1.

Referring now to FIGURE 3, the circuit shown in FIGURE 2 has beenmodified by the inclusion of a diode 34 between the inductor 17 and thecollector of the transistor 16, and a capacitor 35 connected across theinductor 17, resistor 18 and diode 22. In addition, the collector of thetransistor 16 is connected to the terminal 12 through an inductor 36 inseries with the resistor 37.

FIGURE 3 is particularly useful when the circuit is required to operateon low battery voltages. In FIG- URE 2, the inclusion of the diode 22 inseries with the storage inductor 17 not only results in unnecessarypower loss, but the extra voltage drop across the diode 22 makes it morediflicult to obtain satisfactory performance when the battery voltage isvery low. In FIGURE 3, the firing circuit for the rectifier 23 has beenseparated from the storage inductor, which in this case is of courseconstituted by the inductor 36. In use, when the interrupter 15 closesand the transistor 16 conducts, energy is stored in the main inductor 36and also in the inductor 17 which conveniently carries quite a smallcurrent. When the interruptor 15 opens again, the inductor 36 transfersits charge to the capacitor 21, and the inductor 17 transfers its chargeto the capacitor 35. The diode 34 prevents the inductor 36 from chargingthe capacitor 35. When the capacitor 35 is charged to its peak voltage,which may be much lower than the voltage level in the capacitor 21, itstarts to discharge back into the inductor 17, and the diode 22 becomesreverse biased as before so that the controlled rectifier 23 is fired,and the capacitor 21 discharges to produce the spark.'-

The circuit parameters can be chosen so that thecapacitor 35 reaches itspeak voltage at the same time as the capacitor 21, or before or afterthe capacitor 21 as desired. If the controlled rectifier 23 is firedbefore the capacitor 21 is fully charged and if the capacitor dischargeis oscillatory, it is possible to obtain more than one spark for eachoperation of the interruptor, and this feature is useful for someapplications. It is possible that in some circumstances where it isdesired to obtain more than one spark, the rectifier 23 will not beswitched off properly by the oscillating current when the capacitor 21discharges, but this will not be serious. It would of course be seriousif a spark was missed altogether because the rectifier 23 was notswitched off properly, but this cannot happen with the arrangement shownbecause the rectifier 23 is reverse biased when the transistor 16conducts. It will be appreciated that in both FIGURE 2 and FIG- URE 3,the resistor 33 provides a path for reverse biasing the rectifier 23 aswell as ensuring complete discharge of the capacitor 21.

In the modified form of FIGURE 3 shown in FIGURE 4, the inductor 17 andcapacitor 35 are chosen so that the capacitor 21 discharges before itreaches its peak voltage. Moreover, the resistor 18 is re-positionedbetween the cathode of the diode 34 and the collector of the transistor16, so that the capacitor 35 does not discharge immediately when thecontrolled rectifier 23 switches on, but is able to maintain a positivedrive to the gate of the controlled rectifier for a predetermined periodof time. In addition a diode 38 is connected across the capacitor 21.With this arrangement, the rectifier 23 continues to conduct after ithas been fired until either the residual inductive energy in theinductor 36 is dissipated, or the transistor 16 is switched on. At lowengine speed, the energy in the inductor 36 will be dissipated beforethe transistor 16 is switched on, and the circuit will operate in thesame way as FIGURE 3. However, at high engine speeds appreciablyresidual current will still be flowing in inductor 36 when thetransistor is switched on again. The final current attained in thisinductor during the succeeeding period of transistor conduction will behigher, approximately by this amount, than it otherwise would have been.Since the energy stored in the inductor is proportional to the square ofthe current in it, it will be appreciated that quite a low residualenergy will result in a much higher increase in peak energy stored andtherefore an overall increase in energy available for the spark. In thisway higher sparking speeds are obtainable than would be possibleotherwise. The diode 38 also protects the emitter-base junction of thetransistor 16 from the reverse voltage which may be developed oncapacitor 21 in the absence of this diode.

In a further modification of any of the examples shown, the transistor16 is replaced by the interrupter 15 itself.

In all the examples the storage inductor is connected directly to thestorage capacitor, but in a modification the coupling is indirect by wayof a transformer the primary winding of which is constituted by thestorage inductor. In one such arrangement for producing sparks at a lowvoltage plug, the secondary winding of the transformer has one endconnected through the plug to the anode of the rectifier 23, the cathodeof which is connected to the other end of the secondary winding throughthe diode 22. The capacitor 21 is connected across the secondary windingin series with the diode 22, the cathode of which is connected to thegate of the rectifier 23. The diode 22 and the plug are bridged byresistors, and the operation is similar to the circuits described above.It should be noted that the rectifier 23 is still reverse biased throughthe transformer when the transister 16 conducts.

It will be noted that if the transistor 16 is turned on while therectifier 23 is still conducting, there will be a delay before therectifier 23 is reverse biased as a result of inductance in the circuit.In the case of FIGURE 4, a delay of predetermined length can beintroduced deliberately to reduce the risk of production of a spark as aresult of accidental closure of the contacts 15.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A spark ignition circuit for an internal combustion engine,comprising in combination: I

(a) a DC. source;

(b) switch means which is turned on and off in timed relationship to theengine;

(c) a first inductor connected in series with said switch means acrossthe DO. source, energy being stored in said first inductor when saidswitch means is closed;

(d) a first capacitor;

(e) a first charging circuit coupling said first capacitor with saidfirst inductor, said first charging circuit transferring energy fromsaid first inductor to said first capacitor when said switch meansopens;

(f) a discharge circuit connected across said first capacitor andincluding a switch and spark producing means which produces a spark whensaid first capacitor discharges through said switch;

(g) a second inductor connected in series with said switch means acrossthe DC. source;

(h) a second capacitor;

(i) a second charging circuit coupling said second capacitor with saidsecond inductor, said second charging circuit transferring energy fromsaid second inductor to said second capacitor when said switch meansopens whereby said second capacitor charges and then commences todischarge through said second charging circuit;

(j) means in said second charging circuit operable upon commencement ofdischarge of said second capacitor for turning said switch on wherebysaid first capacitor discharges through said discharge circuit toproduce a spark whilst said switch means is still open.

2. A system as claimed in claim 1 in which said switch is a controlledrectifier having its anode and cathode connected in said dischargecircuit.

3. A system as claimed in claim 2 in which said means in said secondcharging circuit is a diode with its anode and cathode connectedrespectively to the cathode and gate of the controlled rectifier, thearrangement being such that when the second capacitor starts todischarge the voltage across the diode turns the controlled rectifier 4.A system as claimed in claim 2 including a resistor in the gate circuitof the controlled rectifier.

5. A system as claimed in claim 3 in which the capacitor is connectedacross said D.C. source in series with said switch means so that energyis transferred directly from the first inductor to the first capacitor.

6. A system as claimed in claim 3 including a third diode between thefirst capacitor and the switch means providing a charging 'path for thefirst capacitor.

7. A system as claimed in claim 6 including a first resistor connectedacross the third diode.

8. A system as claimed in claim 3 including a fourth diode in serieswith the second inductor and switch means for preventing transfer ofenergy from the first inductor to the second capacitor.

9. A system as claimed in claim 3 including a second resistor in serieswith the second inductor and switch means.

10. A system as claimed in claim 9 in which the connection from the gateof the controlled rectifier to the cathode of the first-mentioned diodeis by way of the second resistor.

11. A system as claimed in claim 3 in which the second series circuitturns the controlled rectifier on while the storage capacitor is stillcharging, and provides gate current to the controlled rectifier for apredetermined period of time, so that current flows through thecontrolled rectifier until either the energy stored in the storageinductor is dissipated or the switch means closes.

12. A system as claimed in claim 11 including a diode connected acrossthe first capacitor.

References Cited UNITED STATES PATENTS 3,291,110 12/1966 Peters 1231483,297,911 1/1967 Quinn 315214 2,899,632 8/1959 Lawson 323-58 3,150,2869/1964 Quinn 315-209 3,261,339 7/1966 Quinn 123148 3,271,593 9/1966 DeVilbiss 30788.5 3,312,211 4/1967 Boyer 123-148 3,318,296 5/1967 Hufton123148 LAURENCE M. GOODRIDGE, Primary Examiner.

